The present invention is related to a wireless communication apparatus, and more specifically, a transmission output correcting apparatus for correcting a frequency characteristic of a transmission output.
In a wireless communication apparatus, when transmission output levels are varied in response to frequencies, communicatable distances become unstable, and thus, such an unfavorable phenomenon that communications are interrupted may occur. To avoid such an unfavorable phenomenon, in the conventional wireless communication apparatus, while a variable gain amplifier is employed as a portion of a transmission circuit, transmission power is corrected by variably controlling an amplification gain in response to a frequency.
FIG. 10 is a block diagram of a transmission circuit equipped with the above-described variable gain amplifier. In this drawing, a high frequency signal is amplified by a variable gain amplifier 91, a transmission signal having only a transmission frequency range may pass through a filter 92, and then, the filtered signal is amplified by a power amplifier 93 to a required transmission output level. Thereafter, the amplified signal is outputted to an antenna (not shown) via a filter 94 capable of compensating for a characteristic of the antenna. Normally, while the power amplifier 93 owns an inverse-V-shaped type frequency characteristic as indicated in FIG. 11A, the gain of the variable gain amplifier 91 is variably controlled in order to correct this inverse-V-shaped type frequency characteristic as a flat characteristic as being permitted as possible. Conventionally, while the frequency range is subdivided into a plurality of frequency blocks, the gain of the variable gain amplifier 91 is controlled in order to obtain a desirable transmission output level with respect to each of these frequency blocks, and the controlled gain is stored into a storage unit 96. When a signal transmission operation is carried out, the stored value is read by a control unit 97 to control the gains. FIG. 12 represents an example of a transmission output level which is corrected by the conventional transmission circuit with employment of such a circuit arrangement.
However, as shown in FIG. 12, in the above-described related art, the frequency characteristic within the respective frequency blocks are not made flat, but the discontinuous frequency characteristic is obtained in the overall frequency range. To improve this discontinuous frequency characteristic, although the frequency range may be furthermore subdivided into narrower frequency blocks, the following problem may occur. That is, a total number of data which should be previously stored into the storage unit 96 is increased, and moreover, lengthy time is required for gain controls.
Also, while the frequency characteristic of the transmission output level is also changed, depending upon temperature characteristics of components which constitute the transmission circuit, this frequency characteristic will be varied, for example, as represented in FIG. 11B. As a result, there is such a problem that the high precision correction of the transmission output level can be hardly carried out by merely subdividing the frequency range into the plural frequency blocks so as to correct the transmission output levels with respect to the respective frequency blocks.